NO159641B - HYDROGENATION CATALYST OF PALLADIUM AND RHENIUM ON A CARBON CARBON, PROCEDURE FOR THE PREPARATION OF THIS, AND PROCEDURE FOR THE PREPARATION OF TETRAHYDROFURAN, 1,4-BUTANDIOL OR MIXTURES THEREOF. - Google Patents

Abstract

Palladium/rhenium-on-carbon catalyst; a method employing said catalyst to produce tetrahydrofuran, 1,4-butanediol or mixtures thereof in selectable ratios from a number of starting reactants; and a method for making the Pd/Re/C catalyst.

Description

The present invention relates to a hydrogenation catalyst of palladium and rhenium on a carbon carrier, a method for producing this, and a method for producing tetrahydrofuran, 1,4-butanediol or mixtures thereof by hydrogenating a number of hydrogenable precursors such as maleic acid, maleic anhydride, fumaric acid, succinic acid , malic acid, dimethylsuccinate, Y-butyrolactone or mixtures thereof. These precursors can be described as dicarboxylic acids, dicarboxylic acid esters, lactones or mixtures of indicated acids, esters, lactones and/or anhydrides.

Also a continuous catalytic process for the production of tetrahydrofuran, 1,4-butanediol or mixtures thereof from a normal C 1 -hydrocarbon such as n-butane is described in the following.

A number of methods for the production of tetrahydrofuran and 1,4-butanediol have been described. There are publications relating to the hydrogenation of maleic acid or maleic anhydride which also describe various attempts to maximize product yields. Reference is made in this context to US patents 4,155,919, 3,957,827, 3,370,067 and 3,133,138; Japanese Patent Publications 32439/74 and 43683/69; German patents 2 519 817 and 2 715 66 7, and British patent 1 5 34 2 32. The following publications describe catalytic processes for the production of maleic acid/maleic anhydride: US patents 4 251 390, 4 231 943, 4 244 878 and 4 283 288.

French patent document 2,505,819 describes hydrogenation reactions using stored Pd/Re catalysts. Although the catalysts can be prepared by sequential deposition of Pd and Re metal, no intermediate reduction is described.

The described methods use a selected catalyst to produce high yields of tetrahydrofuran and 1,4-butanediol with high productivity. The processes proceed from dicarboxylic acid or dicarboxylic acid ester starting reactants. By means of the present hydrogenation catalysis-

tor, the process can be directed, as desired, towards the production of high ratios of tetrahydrofuran to 1,4-butanediol and vice versa.

The invention thus relates to a hydrogenation catalyst of palladium and rhenium on a carbon support, which catalyst is characterized in that the catalyst comprises 0.5 to 10% palladium and 1 to 10% rhenium by total weight, where the palladium is present in the form of crystallites of an average size of 10 nm to 25 nm and where the rhenium is present in the form of a highly dispersed phase of crystallites with an average size of less than 2.5 nm. A preferred catalyst contains 1 to 6% Pd and 3 to 6% Re, and a particularly preferred catalyst contains approx. 3% Pd and approx. 3% Re.

The Pd crystallite size has been determined by H2/02 titration, and the Re crystallite size by scanning transmission electron microscopy (STEM).

The highly dispersed Re crystallites are too small to be detected by X-ray diffraction or STEM.

The invention also relates to a method for the production of a hydrogenation catalyst of palladium and rhenium on a carbon carrier, which method is characterized in that it comprises the following steps: (i) impregnation of the carbon carrier with a source of palladium, which palladium is in solution, (ii) removing the solvent and heating the palladium-impregnated carbon to a temperature of 150 to 550°C under reducing conditions, (iii) adding to the palladium-impregnated carbon a source of rhenium in solution, and (iv) removing the solvent from step ( iii), (v) heating the catalyst from step (iv) to a temperature of 150 to 550°C under reducing conditions.

It is preferred to heat the Pd/Re/C catalyst

from step (iv) to a temperature of 150 - 550° C, preferably 200 to 300° C under reducing conditions, usually for 2 to 5 hours. This reduction can be carried out immediately after step (iv), or can be carried out in the hydrogenator just before the reaction is carried out or simultaneously with the start of the reaction.

It is preferred to have a Group IA or IIA metal such as potassium, sodium, lithium, calcium or magnesium present during the catalyst synthesis. Preferred amounts are 0.1 to 1 mol% based on the number of moles of carbon in the carrier. Preferred carriers have a surface area above 650 m <2>/g and preferably

2

over 900 m/g.

The invention also relates to a method for the production of tetrahydrofuran, 1,4-butanediol or mixtures thereof from an oxidizable maleic anhydride precursor comprising oxidizing the precursor to form maleic anhydride and reacting the maleic anhydride with hydrogen in the presence of a hydrogenation catalyst, which method is characterized in that it comprises : (i) collecting the maleic anhydride from the oxidation step in water while forming an aqueous solution of maleic acid, and (ii) reacting the aqueous solution of maleic acid with hydrogen in the presence of a catalyst according to claims 1 and 2.

The reaction temperature is 130 to 285°C, the hydrogen pressure 2 MPa to 35 MPa, the hydrogen space time 1 to 10 minutes and the contact time 0.5 to 7 hours. Representative organic media include dioxane, 7-butyrolactone and the like. The preferred precursors are maleic acid and maleic anhydride.

The catalyst according to the invention provides (a) essentially 100% conversion of the precursors, (b) high selectivity towards and high yield of THF/BD0 product, and (c) the advantage that it is able to control the product ratio THF/BDO by variation of the temperature, contact time and/or hydrogen space time within the described operational areas so that generally the higher the temperature, the longer the contact time, and/or the higher the hydrogen space time, the higher the ratio of THF to BD0 and vice versa. Hydrogen space time is defined as the reaction volume divided by the hydrogen flow rate under reaction conditions.

A continuous process for the production of tetrahydrofuran, 1,4-butanediol or a mixture thereof from a normal C4 hydrocarbon or an aromatic hydrocarbon comprises: (i) oxidation of the hydrocarbon to form maleic anhydride, (ii) collection of the maleic anhydride product from step

(i) in an aqueous solution, and

(iii) reaction of the aqueous solution of maleic acid with hydrogen in the presence of the Pd/Re/C catalyst according to the invention under the described conditions.

It is the essentially complete conversion of maleic acid and the high selectivity to and yield of THF/BDO in an aqueous medium achieved with the carbon-burnt palladium-rhenium catalyst that makes this continuous process efficient and applicable.

A method of preparing the catalyst comprises (a) applying a solution of a palladium compound to a carbon support and removing the solvent; (b) heating the carbon impregnated with the palladium compound formed in (a) to a temperature of 150 to 550° C, preferably 200 - 300° C, under reducing conditions, cooling the carbon-supported palladium material (Pd/C) produced in (b), and (c) applying a solution of a rhenium compound to said material and removing the solvent.

It is preferred to heat the Pd/C impregnated with the rhenium compound formed in step (c) to a temperature of 150 to 550°C, preferably 200 to 300°C under reducing conditions for 2 to 5 hours. This can be carried out immediately after step (c), or can be carried out in the hydrogenation apparatus just before the reaction is carried out or simultaneously with the start of the reaction.

Preferably, production of the Pd/Re/C catalyst is carried out in the presence of Group IA or IIA metals such as potassium, sodium, lithium, calcium or magnesium. The latter can be present in the carbon obtained, or can be added - if absent - by impregnating the carbon carrier with a solution of a metal compound from Group IA or IIA, for example LiCl, NaCl, KCl, KOH, NaOH, CaCl2 or MgCl2 '6H20. It is believed that the Group IA or IIA metal has a beneficial effect on the catalyst microstructure.

Alternatively, the Group IA or Group IIA metal can be added together with the palladium by adding the Group IA or Group IIA metal1 compound to the solution of the palladium compound, or by using a palladium compound that also contains the Group IA or Group IIA metal, for example K2PdCl4 or Na2PdCl4- It is preferred to add the Group IA or Group IIA metal to the carbon support and calcine the impregnated carbon at temperatures in the range of 200 to 400°C for 2 to 6 hours before impregnating the carbon support with the source of palladium.

The solutions of the palladium compound and the rhenium compound can be added to the carbon by dipping or suspending the carrier material in the solution, or by spraying the solution on the carbon. The solution containing the palladium compound is typically an acidic aqueous medium containing HCl and an amount of palladium compound sufficient to give a catalyst product with the required amount of palladium. The palladium compound is typically PdCl 2 , but can also be a palladium compound such as a nitrate, carbonate, carboxylate, acetate, acetylacetonate or amine. The solution containing the rhenium compound is typically an aqueous solution containing an amount of the rhenium compound sufficient to give a catalyst product with the required amount of rhenium. The rhenium compound is typically Re 2 O 4 , but may be a perrhenate of ammonium or of an alkali metal.

Heating under reducing conditions means heating in a reducing environment, preferably hydrogen. Typically, the sample has been reduced by first heating in flowing He at 150° C for 1 hour, then heating to 150° C in flowing He/H2 (50:50 molar ratio) for 1 hour and finally heating to 150° to 550 ° C in flowing He/H2 (50:50 molar ratio) for up to 3 hours.

When a Group IA or Group IIA metal is present in the carbon support during catalyst preparation, large (about 0.2 um) crystallites of the salts of ReO~ are present in the catalyst as observed by X-ray diffraction and transmission electron microscopy. If this catalyst is further exposed to reducing conditions, e.g. during the hydrogenation of maleic acid and then reexamined, no salts of ReO~ or any phase containing a salt of Group IA or Group IIA can be detected. However, the catalyst is still comprised of Pd and Re crystallites as described here.

When the starting reactant is a normal C4 hydrocarbon, the process proceeds without the need for equipment, energy and reaction time which is usually required to isolate and purify the maleic anhydride as described in known hydrogenations. A typical method of carrying out the process comprises (a) reaction of n-butene or benzene in an oxygen-containing gas in the presence of a vanadium/phosphorus mixed oxide catalyst to oxidize in the vapor phase the n-butene to maleic anhydride, (b) collection of the maleic anhydride by a water treatment to form maleic acid in an aqueous solution in a concentration of approx. 40% by weight, and (c) reacting the solution obtained in (b) with hydrogen in the presence of the Pd/Re/C hydrogenation catalyst.

Preferably, oxidation steps are carried out. (a) at a temperature of 300 to 600° C and a pressure of 50 to 2000 kPa, and hydrogenation step (c) is carried out at a temperature of 150 to 275° C and a hydrogen pressure of 2 MPa to 35 MPa.

The liquid phase hydrogenation can

is carried out using conventional equipment and technology in a stirred tank reactor or in a reactor with a stationary bed. Hydrogen is added continuously, generally in significant stoichiometric excess without any inert diluent gas.

Unreacted hydrogen can be returned to the reactor as a recirculation stream. The precursor solution, e.g. maleic acid solution, is fed continuously in concentrations varying from dilute solutions to approximately maximum solubility, typically 30 to 40% by weight. The catalyst's carbon carrier has a particle size of approx. 200 mesh for use in a stirred tank reactor or are larger carrier granules (0.64 cm) to 60 mesh for use in a fixed bed reactor. The required amount of catalyst will vary widely and is dependent on a number of factors such as reactor size and design, contact time and the like. For a 60 cm 2 reactor, for example, 25 g of the preferred catalyst, 3% Pd/3% Re/C, is used.

The following examples illustrate the invention. Temperatures are given in degrees Celsius unless otherwise stated. Unless otherwise stated, all hydrogenation experiments were carried out in a reactor with a diameter of 1.27 cm and a length of 76 cm. The reactor was constructed from BWG 20, 1.2 7 cm Hastelloy C tubing with wall thickness 0.0 9 cm, ID = 1.1 cm. The reactor volume was calculated based on the packed catalyst volume. For all examples, the packed layer length was 6 3 cm. The hollow volume was filled with inert silicon carbide. The resulting catalyst reaction volume was calculated to be 59.49 cm, which is the value used for determining the surface reaction residence time, i.e. the contact time.

The reactor was operated in a co-current, upstream fashion. Liquid maleic acid or any of the other precursor starting materials and hydrogen were measured separately and then introduced into a mixing T-tube at the bottom of the reactor. Initial mixing, as well as preheating, was carried out in an inert, packed bed section. Products as well as excess hydrogen were removed through a valve in which the pressure was reduced down to atmospheric pressure from the reaction pressure. The collected liquid was the main amount of product containing tetrahydrofuran (THF) and 1,4-butanediol (BDO) with smaller amounts of by-product. The reaction vapor stream was passed through a series of vapor/liquid release vessels: the first held at room temperature followed by a water/ice trap, followed by two (in series) dry ice/acetone traps. The collected product was primarily THF with smaller amounts of raono-alcohols and butyrolactone. These traps were used ■ because of the difficulty of using liquid/vapor release vessels on a small scale.

Unless otherwise stated, the maleic acid feed was prepared by adding 500 g of certified grade maleic anhydride (Fisher Scientific Co.) to 1190 g of distilled water. The hydrogen was taken from hydrogen cylinders with 99% purity and was compressed to a reaction pressure of 17 MPa. The hydrogen feed rate was 1000 cm<3>/min (STP) which is equivalent to a hydrogen space time of 6 minutes at the reaction conditions, ie 17 MPa and 200° C. Unless otherwise stated, the hydrogen space time was 6 minutes. The catalyst was particulate and had a size of less than 20 mesh. The unit in which the "space-time yield" is expressed in all table headings and examples is g product

kg cat-hr.

Example 1

A 3 wt% Pd/3 wt% Re/carbon loaded catalyst (3% Pd/3% Re/C) was prepared as follows. Calgon PCB 12 x 30 carbon was calcined at 200°C for 2 hours and then at 400°C for 2 hours. This treated carbon had a surface area of 1000 to 1300 m<2>/g with a pore volume of

0.6 cm<3>/g. A sequential deposition of Pd and Re on the treated carbon was carried out as follows: 50 g of the treated carbon was added to a solution of 2.5 g of PdCl2 in 10 ml of concentrated HCl and 80 ml of distilled water. After 3 hours at room temperature with occasional stirring, the slurry was dried for 18 hours at 110°C.

The sample was reduced by first heating to 150°C in flowing He (1000 cm/min) for 1 hour, then heating to 150°C in flowing He/H2 (50:50 molar ratio, 1000 cm^/min) for 1 h, and finally heated to 300° C in flowing He/H2 (50:50 molar ratio, 1000 cm<3>/min) for 3 h. The sample was quickly cooled to 50° C in the He/H2 atmosphere. Nitrogen was introduced while the sample was cooled to room temperature. After 30 minutes in flowing nitrogen, the sample was passivated at room temperature by introducing flowing 1:99 (molar ratio) 02/<N>2 for 2 hours.

Then 5 g of Re 2 O 3 was added to 50 ml of distilled water and then 19.7 ral of this solution and 70 ml of distilled water were introduced into a 1000 ml flask together with 50 g of Pd/C catalyst. After 3 hours at room temperature with occasional stirring, the slurry was dried, reduced and passivated in the same way as described for the Pd/C catalyst. The resulting material was the 3% Pd/3% Re/C catalyst.

The Pd/Re/C catalyst prepared according to this example was examined by X-ray diffraction, transmission scanning electromicroscopy and H2/C>2 titration and was found to have palladium crystallites with an average size of

150 Å to 200 Å (15 to 20 nm). The particles of rhenium were below the size at which they could be detected by X-ray diffraction or by electron transmission scanning microscopy. It was therefore assumed that the rhenium particle size was below 25 Å (2.5 nm).

By the described microscopy and crystallographic techniques, KReO 4 crystallites with an average size of 0.2 µm were detected. Microscopy observations showed that the highly dispersed rhenium phase of small crystallites discussed above is in contact with some palladium crystallites. The carbon carrier used in the production of this catalyst contained 0.36 mol% K.

Example 2- 14

The 3% Pd/3% Re/C catalyst prepared as described in Example 1 was filled into a reactor with a diameter of 1.27 cm. The maleic acid feed rate was adjusted to give contact times of from 0.9 h to 5.5 h (for example, in a maleic acid feed rate of 0.5 cm<3>/min a reaction or contact time of 2.0 h) and hydrogen - the flow rate was adjusted to give a hydrogen rotation time of either 3 or 6 minutes. The hydrogenation reaction was carried out at reaction temperatures of 175° C, 180° C, 190° C, 200° C, 215° C and 225° C. Samples of the reaction product were taken continuously. The distribution of product THF and BDO and mono-alcohol by-product such as butanol, propanol etc. and Y-butyrolactone intermediate in mol% based on the carbon species is shown in Table 1 for the different reaction conditions. These are the average values of several measurements taken after the equilibrium conditions were reached.

No detectable amount of maleic acid was found, indicating that essentially all of it was converted. Therefore, the mole percent shown is the selectivity as well as the yield of the particular component. Also shown is the space-time yield. The space-time yield is the amount of product obtained per time unit per unit weight introduced metal catalyst. The results show that high selectivity to and high yield of THF/BDO is achieved and that the THF/BDO product ratio increases as the temperature increases, as the contact time increases and/or as the hydrogen space time increases, and that the product ratio can be adjusted over a range from essentially only BDO to mainly just THF.

Example 15-18

A 1% Pd/3% Re/C catalyst was prepared using the method described in Example 1 with the exception that the amount of PdCl2 was 1/3 of that required and that the highest temperature in the reduction after Pd -deposition was 350° C, and that the highest temperature during the reduction after the Re-deposition was 150° C.

The hydrogenation was carried out as described in Example 2-14 with a reaction temperature of 180° C. The maleic acid flow rate was adjusted so that the contact time varied from 2.1 to 3.5 hours. The results given in Table 2 show that the THF/BDO product ratio increased as the contact time increased.

Example 19-24

A 3% Pd/1% Re/C catalyst was prepared by the method described in Example 1, with the exception that the amount of Re 2 O 3 was 1/3 of that noted in Example 1. The hydrogenation was carried out as described in Example 2-14 with different reaction temperatures and reaction contact times. The results shown in Table 3 show that increased reaction temperature and/or increased reaction contact times result in higher THF/BDO. No measurable amount of maleic acid was found, indicating essentially complete conversion.

Example 25

A 10% Pd/3% Re/C catalyst was prepared by the method described in Example 1, with the exception that the amount of PdCl2 was 10/3 of that stated in Example 1. 53.76 g of dimethyl succinate and 6, 0 g of water was placed in a pressure vessel and brought into contact with 30 g of the 10% Pd/3% Re/C catalyst at a hydrogen pressure of 175.7 kg/cm and a temperature of 285° C. for 2 hours. The reaction product based on the carbon species exhibited 62.2 mol% THF, 17.6 mol% butanol, 4.7 mol% propanol and 14.5 mol% Y~butyrolactone.

Example 26 and 2 7

A 3% Pd/3% Re/C catalyst was prepared by the method described in Example 1, with the exception that the highest temperature in both reduction steps was 200° C instead of 300° C. Hydrogenation was carried out as described in Example 2-14, but with the reaction conditions indicated in Table 4. The results show that a longer contact time results in a higher THF to BDO ratio.

Example 28-32

A 3% Pd/3% Re/C catalyst was prepared by the method described in Example 1, with the exception that the reaction step after the palladium deposition was carried out at a maximum temperature of 500° C instead of 300 ° C. The hydrogenation was carried out as described in Example 2-14, but the reaction conditions are indicated in Table 5. The results show the advantages achieved with the catalyst according to the invention.

Example 33

A 6% Pd/3% Re/C catalyst was prepared by the method described in Example 1, with the exception that the amount of PdCl2 was double that indicated in Example 1. The hydrogenation was carried out as described in Example 2 - 14. At a reaction temperature of 180° C and a contact time of 2.1 hours, the product//byproduct distribution in mol% was THF-6 7/BDO-19//monoalcohols-8/Y-butyrolactone-5/ succinic acid-l and the space-time yield was 2 39.

Example 34

A 6% Pd/6% Re/C catalyst was prepared by the method described in Example 1, with the exception that the amount of PdCl2 was double that stated in Example 1. and that the amount of Re2O^ also was twice as large. The hydrogenation was carried out as described in Examples 2 - 14. At a reaction temperature of 180° C and a contact time of 2.0 hours, the product/by-product distribution in mol% THF-4 0/BDO-50/- monoalcohol-9/ γ-butyrolactone-1 and the space-time exchange was 300.

Example 35

The catalyst according to Example 1 was used in a hydrogenation identical to that described in Examples 2 - 14, with the exception that the feed was furic acid in aqueous solution in a concentration of 9% by weight. The reaction temperature was 180°C and the reaction time 2.0 hours. The THF/BDO//moho alcohol/- Btyl distribution in mol% was 19/71//8/2. The space-time yield was 72.

Example 36

A continuous process for the production of THF/BDO from n-butane via an unisolated maleic acid intermediate is as follows: Preactivated catalyst with V/P/Ox: 3 atora% with 2 wt% SiO2 in the form of pellets with a diameter of 0.32 cm and which weighed approx. 70 g was charged into a vertical 316 stainless stationary weight reactor of 2.54 cm diameter and 30.4 8 cm height,

which was heated in a fluidized sand bath to achieve temperature control. This reactor was coupled to enable direct transport of (1) the feed stream comprising 1.5% n-butane in air from a feed manifold through a preheating coil contained in the sand bath and then into the bottom of the reactor to contact the catalyst bed, and (2 ) product flow-but through an outlet line heated to a temperature somewhat above 200° C (to avoid deposition of maleic anhydride) and then to a splitter which led approx. 80% of the waste gases through water to absorb out the maleic anhydride for subsequent hydrogenation.

The remaining portion of the product stream was transported through a heated line to a dual gas chromatograph (GC) for product analysis. Introduction of a heated back pressure valve in the outlet line above the GC device allowed operation of this system from atmospheric pressure

(100 kPa) to a maximum of 870 kPa. Operating temperatures

were in the range of 380 to 450°C and contact times, expressed at standard temperature and pressure, in the range of 1 to 7 seconds.

The analytical device enabled the determination of N2, 02,

CO, C02, H20, n-butane, maleic anhydride, ethylene, furan, methyl-ethyl-ketone, acetic acid, and acrylic acid. The maleic acid solution was colorless.

Hydrogenation of impure maleic acid intermediate

was carried out as described in Examples 2-14 using the 3 Pd/3% Re/C catalyst of Example 1. The maleic acid concentration was 33% by weight and the maleic acid feed rate was 0.5 cm<3>/min corresponding to a contact time of 2 hours. The reaction temperature was 200° C. The product/by-product (THF/BDO//monoalcohol) distribution in mol% was 30/58//12. The space-time yield was 2 80.

Example 3 7 and comparative examples A and B

This example and the comparative examples were carried out to demonstrate the activity of a catalyst according to the invention (Example 37) against the lower activities of two catalysts outside the scope of the invention (Examples A and B).

In the example and in the comparative examples, the catalyst comprised 3 wt% Pd and 3 wt% Re stored on carbon. The catalyst according to the invention was prepared as described in Example 1.

The catalyst according to comparative example A was prepared as follows: iOO g of activated carbon was calcined in an air atmosphere, first at 200° C. for 2 hours, then at 400° C. for 2 hours. The carbon was cooled and then sieved resulting in 54.0 g of calcined carbon, 20 mesh. A 0.0 76 g Re/ml solution was prepared by adding 5.0 g Re2Oy

to 50 ml of distilled water. Then 19.7 ml of the solution, 10 ml of concentrated HCl, 50 ml of distilled water, 2.5 g of PdCl2 and

50 g of calcined carbon added to a 1000 ml flask. After

After 3 hours with occasional stirring, the slurry was dried at 110° C. for 18 hours. The Pd/Re/C catalyst was then reduced by the following procedure: Heating to 150°C in nitrogen for 1 h, then to 150°C in 50%/50% N2/H2 for 1 h, then to 300°C for 50 %/50% N2H2 for 3 hours. After cooling, the catalyst was passivated in a 1% O 2 /N 2 atmosphere for 3 hours.

The catalyst according to comparative example B was prepared as follows: 100 g of activated carbon was calcined in an air atmosphere, first at 200° C. for 2 hours, then at 400° C. for 2 hours. The carbon was cooled and then sieved resulting in 61.0 g of calcined carbon, 20 mesh. A 0.076 g Re/ml solution was prepared by adding 5.0 g Re-jO^

to 50 ml of distilled water. Then 19.7 ml of the solution was added to a 1000 ml flask and 50 g of calcined carbon and 70 ml of distilled water were added. After 4 hours with occasional stirring, the slurry was dried at 110° C. for 18 hours.

The Re/C material was reduced by the following method: Heating to 150°C in nitrogen for 1 hour, then to 150°C

in 50%/50% N2/H2 for 1 hour, then to 300° C in 50%/50%

N2H2 for 3 hours. The Re/C material was passivated in 1% 02/N2

1 3 hours. Then 2.5 g of PdCl 2 , 70 ml of distilled water and 10 ml of concentrated HCl were introduced into a 1000 ml flask. The Re/C material was added to the solution and the slurry was allowed to stand at ambient temperature for 3 hours. The slurry was dried for 18 hours at 110°C and was reduced under the following conditions: Heating to 150°C in nitrogen for 1 hour, then to 150°C in 50%/50% N2/H2 for 1 hour, then to 300° C in 50%/50% <N>2/<H>2 for 3 hours. After cooling, the catalyst was passivated in 1% O 2 /N 2 for 3 hours. The hydrogenation was carried out as follows: In each case, the carbon-supported catalyst containing 3% Pd and 3% Re, weighing 18 g, was filled into a Hastelloy C, high-pressure reaction tube with a diameter of 0.94 cm and a length of approx. 60 cm. The reaction tube was heated with a three-zone electric vertical oven. A nitrogen purge of the reaction system was completed and the reactor was then compressed to 175.8 kg/cm 2 with hydrogen. A steady hydrogen flow of 2 1/rain, S.T.P., was maintained while the reactor was slowly heated to the temperature at which the reaction was to take place, and was held for 1 hour to effect catalyst conditioning. When conditioning was complete, a 35% by weight maleic acid solution was introduced at a given flow rate. The reactants were introduced co-currently in the upstream direction. Reaction products and excess hydrogen were removed through a back pressure control valve, where samples of the reaction product were taken every half hour.

The microstructure of the catalyst produced by the method according to comparative example A in which Re and Pd were deposited simultaneously comprised Pd crystallites with an average size of only 7 nm and a highly dispersed Re phase. After use, the Pd crystallites were larger and were detected by X-ray diffraction, but no metallic Re could be detected. The microstructure of the catalyst according to comparative example B hbori Re and then Pd were deposited in order, comprised Pd crystallites with an average size of only 8 nm and Re in large crystallites with an average size of 50 nm before use. In addition, contact between Pd and Re phases was not evident. After use, the Pd and Re phases were amorphous and thus could not be detected by X-ray diffraction.

The reaction temperatures, contact times and product//byproduct//feed distributions are shown in Table 6. It is observed that the catalyst according to the invention gives complete maleic acid conversion and high selectivity towards THF/BDO, while the catalysts according to comparative examples A and B give incomplete conversions and low selectivities.

Example 38-47

The following examples were carried out with the catalyst of Example 1 to demonstrate the use of different starting materials, different strengths of solutions, and water and organic solvents. The starting materials, the solutions and the reaction conditions and the results are shown in Tables 7 and 8. The hydrogen space time was 6 minutes in all cases.

Comparative example C

Example 1 was repeated with the assumption that the carbon support was leached with HCl to reduce the level of K to less than 0.001 mol% before the deposition of Pd and the catalyst microstructure was changed in that the Pd crystal size, as determined by H2/O2 titration, was only approx. 5 nm. Hydrogenation by the general procedure described in example 2-14 at a temperature of 180° C and a residence time of 2 hours and 2.2 hours gave a selectivity of 13/79 (THF/BDO) and a space-time yield of 325 with the catalyst according to Example 1 against a selectivity of 33/19 (THF/BDO) and a space-time yield of 210 with the catalyst from which K was excluded.

Example 4 8

A 3 wt% Pd/3 wt% Re/carbon supported catalyst in which 0.5 mol% sodium was added to the potassium leached carbon was prepared in the following manner. Calgon^

PCB 12 x 30 carbon was calcined at 200°C for 2 hours and then at 400°C for 2 hours. Ash and fine particles were separated by sieving on a 20 mesh sieve. Then 200 g of the resulting carbon was added to 4 liters of 1M HC1. The slurry was allowed to stand for 24 hours. The carbon was then collected on a filter funnel and washed with 4 liters of distilled water. The acid wash was repeated and the carbon was then dried at 110° C. for 18 hours. The yield was 190.3 g of potassium leached carbon. The potassium-free carbon (50.0 g) was added to a solution of 1.3 g of NaCl in 70 ml of distilled water. After 3 hours at room temperature with occasional stirring, the slurry was dried at 110° C. for 18 hours. Carbonate with added Na was added to a solution of 2.5 g of PdCl2 and 10 ml of concentrated HCl in 65 ml of distilled water. After 3 hours at room temperature with occasional stirring, the slurry was dried at 110° C. for 18 hours. The Pd/C sample was then heated for 1 h to 150°C in helium at 100 cm<3>/min, then for 1 h to 150°C in helium/hydrogen at 100 cm<3>/min each, and finally for 3 hours at 300° C in the same helium/hydrogen atmosphere. After cooling in flowing helium/hydrogen, the solid material was passivated with 1.5% oxygen in nitrogen for 18 hours.

The passivated solid Pd/carbon (48.3 g) was added to a solution of 19 mL of 0.2 M Re 2 O 7 in 51 mL of water. After 3 hours at room temperature with occasional stirring, the slurry was dried at 110° C. for 18 hours. The sample was then reduced and passivated as described above, and 47.8 g of Pd/Re/C catalyst was prepared.

The hydrogenation was carried out using 27 g of this catalyst with a 35% by weight aqueous solution of maleic acid at a temperature of 190° C, an H2 pressure of 17 mPa, a contact time of 2.2 hours and a hydrogen space time of 6.0 minutes. The reaction product in mol% based on the carbon parts was THF-55BDO-34//monoalcohols-8/7-butyrolactone-3, and the space-time yield t was 24 0.

Examples 49 to 51

A 3 wt% Pd/3 wt% Re/carbon supported catalyst was prepared as follows: 100 g of Westates CC-521-G carbon was added to a solution of 9.6 g of Na2PdCl4•3H20 in 86 ml of distilled water. After 1 hour at room temperature, the slurry was dried with stirring using a steam bath. The carbon was impregnated with 4.0 g of NaOH in 88 ml of distilled water for 2 hours. The carbon was then washed with distilled water until it was chloride-free, and 150 g of Pd-on-carbon sample was recovered after drying. 45 g of the material was dried at 110° C. for 18 hours. It was then heated for 1 hour at 150°C in He flowing at a rate of 100 cm/min, followed by 1 hour at 150°C in helium/hydrogen each at 100 cm<3>/min, and finally in 3 hours at 300° C in a flowing helium/hydrogen atmosphere. After cooling under flowing helium/hydrogen, the sample was passivated with 1.5% oxygen in nitrogen for 18 hours. Then 29.38 g of the reduced Pd/C was added to a solution of 11.5 g of 0.2 M Re-^O^ Q in 38.5 ml of distilled water. After 3 hours at room temperature, the slurry was dried at 110° C. for 18 hours. The resulting Pd/Re/C catalyst was reduced and passivated as described above to yield 29.44 g of catalyst.

The hydrogenation was carried out as described in Example 2-14 with the reaction temperatures and contact times shown in Table 9. The hydrogen pressure was 17 MPa and the hydrogen space time was 6.0 minutes for all three examples.

Comparative example D to H

Sequential Pd/Re deposition without intermediate reduction

A catalyst composed of 3 wt% Pd and 3 wt% Re stored on carbon was prepared in the following way.

100 g of carbon (Calgon PCB 12 x 30) was calcined at 200°C for 2 hours and then at 400°C for 2 hours. Then 65.25 g of the carbon was recovered on a 20 mesh sieve. Sequential deposition of Pd and Re on the recovered calcined carbon was carried out as follows: 50 g of the calcined carbon was added to a solution of 2.5 g of PdCl 2 and 10 ml of concentrated HCl in 75 ml of distilled water. After 3 hours at room temperature with occasional stirring, the slurry was dried at 110°C for 18 hours, 1 g of the dried Pd/C sample was removed for analysis, and the residue, 50.31 g, was added to 19.86 mL of a solution of 0/2 M Re 2 O 7 1 65 ml distilled water. After 3 hours with occasional stirring at room temperature, the slurry was dried at 110°C for 18 hours. 1 g of the dried Pd/Re/C sample was removed for analysis, and the residue was heated at 150°C for 1 h in 100 cm~Vmin helium, and then at 150°C for 1 h in 100 cm 3 /min each of helium and hydrogen, and finally at 300°C for 3 hours in a flowing He/H2 atmosphere. The sample was then cooled to room temperature. The reduced Pd/Re/C sample was passivated in 1.5% oxygen in nitrogen for 18 hours. The yield was 46.68 g of passivated, reduced Pd/Re/C catalyst.

The hydrogenation was carried out as described in Examples 2 to 14 with the reduction temperatures, reaction contact times and results shown in Table 10, which results show incomplete conversion and low selectivities.

Examples 52 to 56

400 g of carbon (Calgon PCB 12 x 30) was added

1 M HCl. After 24 hours, the carbon was collected on a filter funnel and was then washed with distilled water until it was free of chloride. The acid treatment and washing were repeated, and the carbon was then dried at 110°C for 48 hours. The acid-washed carbon was recovered in an amount of 385.3 g and was then used as follows.

A catalyst comprising 3% Pd/3% Re/C containing 0.30 mole percent Mg (Example 52) was prepared as follows. First, 96.0 g of the acid leached carbon was added to a solution of 4.82 g of MgCl 2 -6H 2 O in 150 ml of distilled water. After 3 hours at room temperature with occasional stirring, the slurry was dried with frequent stirring at 110°C for 18 hours. The Mg/C sample was calcined at 200°C for 2 hours and then at 400°C for another 2 hours. The resulting calcined Mg/C sample was collected on a 20 mesh sieve.

50.0 5 of the calcined Mg/C was added to a solution of 2.5 g PdCl 2 + 10 ml concentrated HCl in 75 ml distilled water. After 3 hours at room temperature, the slurry was dried with frequent stirring at 110°C for 18 hours. The Pd/C-Mg sample was then reduced by heating to 150°C for 1 hour in 100 cm<3>/min helium, then to 150°C for 1 hour in 100 cm 3/min each of helium and hydrogen, and finally at 300 o C for 3 hours in flowing helium/hydrogeyn<.> The sample was cooled to room temperature in flowing helium/hydrogen and was then passivated in 1.5% 02/N2 for 18 hours.

Then 47.95 g of the reduced Pd/C-Mg sample was added to 19 ml of 0.2 M Re 2 O 7 and 60 ml of distilled water. After 3 hours at room temperature, the slurry was dried at 110°C

for 18 hours. The Pd/Re/C-Mg sample was then reduced as described above after the Pd addition, and the reduced Pd/Re/C-Mg catalyst was passivated in 1.5% oxygen in nitrogen for 18 hours. The passivated reduced Pd/Re/C-Mg catalyst was prepared in an amount of 48.34 g.

A catalyst comprising 3% Pd/3% Re/C containing 0.30 mole percent Ca (Example 53) was prepared as follows.

First, 96.0 g of acid leached carbon was added to a solution of 2.66 g of CaCl2 in 150 ml of distilled water. After 3 hours at room temperature with occasional stirring, the slurry was dried with frequent stirring at 110°C for 18 hours. The Ca/C sample was calcined at 200°C for 2 hours, then at 400°C for another 2 hours. The resulting calcined Ca/C sample was collected on a 20 mesh sieve.

50.0 g of the calcined Ca/C was added to a solution of 2.5 g of PdCl 2 + 10 ml of concentrated HCl in 75 ml of distilled water. After 3 hours at room temperature, the slurry was dried with frequent stirring at 110°C for 18 hours. The Pd/C-Ca sample was then reduced by heating to

150°C for 1 hour in 100 cm<3>/min helium, then to 150°C for 1 hour in 100 cm 3/min each of helium and hydrogen, and finally at 300°C for 3 hours in the flowing helium/hydrogen atmosphere. The sample was cooled to room temperature in flowing water

helium/hydrogen and was then passivated in 1.5% 02/N2 for 18 hours.

Then 49.0 g of the reduced Pd/C-Ca sample was added to 19.35 ml of 0.2 M Re 2 O 7 and 65 ml of distilled water. After 3 hours at room temperature, the slurry was dried at 110°C for 18 hours. The Pd/Re/C-Ca sample was then reduced as described above after the Pd addition, and the reduced Pd/Re/C-Ca catalyst was passivated in 1.5% oxygen in nitrogen for 18 hours. The passivated reduced Pd/Re/C-Ca catalyst was prepared in an amount of 50.28 g.

A catalyst comprising 3% Pd/3% Re/C containing 0.30 mole percent K (Example 54) was prepared as follows. First, 96.0 g of the acid-leached carbon was added to a solution of 1.38 g of KOH in 150 ml of distilled water. After 3 hours at room temperature with occasional stirring, the slurry was dried with frequent stirring at 110°C for 18 hours. The K/C sample was calcined at 200°C for 2 hours, then at 400°C for another 2 hours. The resulting calcined K/C sample was collected on a 20 mesh sieve.

50.0 g of the calcined K/C was added to a solution of 2.5 g of PdCl2 + 10 ml of concentrated HCl in 75 ml of distilled water. After 3 hours at room temperature, the slurry was dried with frequent stirring at 110°C for 18 hours. The Pd/C-K sample was then reduced by heating to 150°C for 1 h in 100 cm<3>/min helium, then to 150°C for 1 h in 100 cm 3/min each of helium and hydrogen, and to finally at 300°C for 3 hours in flowing helium/hydrogen, and then passivated in 1.5% ©2/N0 for 18 hours.

Then 48.4 g of the reduced Pd/C-K sample was added to 19.10 ml of 0.2 M Re 2 O 7 and 65 ml of distilled water. After 3 hours at room temperature, the slurry was dried at 110°C for 18 hours. The Pd/Re/C-K sample was then reduced

as described above after the Pd addition, and the reduced Pd/Re/C-K catalyst was passivated in 1.5% oxygen in nitrogen for 18 hours. The passivated reduced Pd/Re/C-K catalyst was prepared in an amount of 48.67 g.

A catalyst comprising 3% Pd/3% Re/C containing 0.36 mole percent Li (Example 55) was prepared as follows. First, 96.0 g of the acid-alcohol carbon was added to a solution of 1.17 g of LiCl in 150 ml of distilled water. After 3 hours at room temperature with occasional stirring, the slurry was dried with frequent stirring at 110°C for 18 hours. The Li/C sample was calcined at 200°C for 2 h, then at 400°C for another 2 h. The resulting calcined Li/C sample was collected on a 20 mesh sieve.

50.0 g of the calcined Li/C was added to a solution of 2.5 g of PdCl 2 + 10 ml of concentrated HCl in 80 ml of distilled water. After 3 hours at room temperature, the slurry was dried with frequent stirring at 110°C for 18 hours. The Pd/C-Li sample was then reduced by heating to

150°C for 1 hour in 100 cm<3>/min helium, then to 150°C for 1 hour in 100 cm/min each of helium and hydrogen, and finally to 300°C for 3 hours in a flowing helium/hydrogen atmosphere . The sample was cooled to room temperature in flowing helium/hydrogen and was then passivated in 1.5% O 2 /N 2 for 18 hours.

Then, 49.5 g of the reduced Pd/C-Li sample was added to 19.5 ml of 0.2 M Re902 and 60 ml of distilled water. After 3 hours at room temperature, the slurry was dried at 110°C for 18 hours. The Pd/Re/C-Li sample was then reduced as described above after Pd addition, and the reduced Pd/Re/C-Li catalyst was passivated in 1.5% oxygen in nitrogen for 18 hours. The passivated reduced Pd/Re/C-Li catalyst was prepared in an amount of 49.97 g.

These catalysts, together with a catalyst prepared according to Example 48 and comprising 3% Pd/3% Re/C containing 0.5 mole percent Na (Example 56), were used in hydrogenation trials carried out as described in Examples 2 to 14 with the reaction temperatures, reaction contact times and results shown in Table 11.

Claims (3)

1. Hydrogenation catalyst of palladium and rhenium on a carbon support, characterized in that the catalyst comprises 0.5 to 10% palladium and 1 to 10% rhenium by total weight, where the palladium is present in the form of crystallites with an average size of 10 nm to 25 nm and where the rhenium is present in the form of a highly dispersed phase of crystallites with an average size of less than 2.5 nm. 2. Process for producing a hydrogenation catalyst of palladium and rhenium on a carbon support, characterized in that it comprises the following steps: (i) impregnation of the carbon support with a source of palladium, which palladium is in solution, (ii) removal of the solvent and heating of the palladium-impregnated carbon to a temperature of 150 to 550°C under reducing conditions, (iii) adding to the palladium-impregnated carbon a source of rhenium in solution, and (iv) removing the solvent from step (iii), (v ) heating the catalyst from step (iv) to a temperature of 150 to 550°C under reducing conditions. 3. Process for the production of tetrahydrofuran, 1,4-butanediol or mixtures thereof from an oxidizable maleic anhydride precursor comprising oxidizing the precursor to form maleic anhydride and reacting the maleic anhydride with hydrogen in the presence of a hydrogenation catalyst, characterized in that it comprises: (i ) collection of the maleic anhydride from oxyda- the ion step in water while forming an aqueous solution of maleic acid, and (ii) reacting the aqueous solution of maleic acid with hydrogen in the presence of a catalyst according to claims 1 and 2.